Over the past decades, legal historians have become more cautious when it comes to rules that in the Middle Ages and the early modern period were defined as ‘(old) customs’. Earlier optimistic appraisals as to the age of such rules have been challenged. This article argues that efforts of debunking should be combined with a more thorough analysis of the legal consciousness of past societies. It proposes to look at old municipal private law, not as a set of rules fixed by tradition, but rather as a malleable body of norms. The symbolic qualities of law were such that renewal and rephrasal could be combined with an ideology of conservation. It was perfectly possible for administrators to promote new rules as being a part of an ‘age-old law’ of the city or the land, without breaching the implicit conventions as to the qualities of law. However, as will be demonstrated further, there were limits to the agency of administrators in this regard. The codes as to the features of law marked boundaries that had to be taken seriously.